Air ducts of various lengths and sizes are used to transfer clean, filtered air from an air filter through an engine air intake system. It is also well known to use air ducts to transfer cooled or heated air from within the engine compartment to the passenger compartment of an automobile. Air ducts are widely used in other applications wherever air or any other gas-like substance is transferred between components.
Air ducts have been formed by using a rubber molding process. Although the rubber molded air ducts are effective, they are considered too heavy for use in vehicles requiring lighter weight to improve fuel efficiency. Additionally, rubber molded air ducts are bulky and difficult to mold in the serpentine configurations desired for automobiles which have limited space in the engine compartment.
An alternative to using a one-piece rubber molded air duct is a two-piece construction which utilizes a thermoplastic blow molded tubular body with an injection molded rubber cuff, sometimes called a seal, affixed to an end thereof. Although lighter and more compact than a rubber air duct, the two-piece construction has its own inherent problems. The tubular body must be mechanically secured or adhesively bonded to the seal to effect a connection therebetween that can withstand the vibration and heat within an engine compartment. Furthermore, the connection between the tubular body and the molded seal tends to break after the air duct has been repeatedly detached and re-attached to the air filter or other receiving port. And the connection is further stressed by the pressurized air flowing through the duct. A complete break in the connection between the tubular body and the seal renders the air duct unusable. Even a slight break between the two parts may allow unwanted impediments to enter the air intake system of the engine. Moreover, the additional manufacturing steps of independently molding the rubber seal and securing the seal to the tubular body adds additional cost to the air duct.
Automotive air ducts are typically made of either hard or flexible polymers depending upon the particular end application. Seals or cuffs are typically made of a very soft elastomeric polymer material. The cuffs are attached to a connection port in many ways including, but not limited to, thermoplastic welding, worm-gear clamping, or overmolding. Overmolding is the most robust process for forming the cuff because it creates a uniform melt bond to the hard polymer duct. However, such configurations are problematic in that when the cuff formed between the hard polymer duct and the softer cuff is under a shear-type load, due to engine motion, or high internal air pressures, the cuff and related seal has a tendency to tear because of their soft nature. One solution to this tearing problem is to utilize a very expensive, reinforced thermoset rubber hose.
However, the reinforced rubber hoses have a tendency to leak at flex points, thus ultimately leading to a failure of the duct and cuff. Therefore, there is a need in the art for an air duct configuration that resists tearing, provides a permanent leak-free cuff, which does not flex and which can be made at a lower cost than a reinforced rubber hose.